The coordinate of an electromagnetic pointer or pen is obtained through the transmitting and receiving of electromagnetic waves between loop antennas on a digitizer and the electromagnetic pointer. Signal values sensed by each loop antenna may alter as the incline angle of the electromagnetic pointer changes. Traditionally, the incline angle of the electromagnetic pointer is determined firstly, and then the incline angle is used to compensate coordinate estimation.
A conventional method for determining an incline angle of an electromagnetic pointer disclosed in U.S. Pat. No. 5,751,229 utilizes a main peak value (i.e., a value of a main peak in a diagram of voltage signal distribution in X or Y coordinates) and a sub peak value (i.e., a value of a sub peak in the diagram of voltage signal distribution in X or Y coordinates) of inductive voltage distribution to calculate the incline angle. However, in this conventional method, when the electromagnetic pointer is perpendicular to X axis and tilts along Y axis, the ratio of the main peak value to the sub peak value will vary because the main peak value and the sub peak value in X axis are changed correspondingly. Therefore, the accuracy of the inclined angle calculation would be affected.
Another conventional method for determining an incline angle of an electromagnetic pointer disclosed in Taiwan patent publication NO. 201128461 utilizes signal peak values at the left side and right side of a position at where the electromagnetic pointer is located, to calculate the ratio of the left peak value to the right peak value such that the incline angle of the electromagnetic pointer is estimated.
Both of the two conventional methods need to scan lots of loop antennas (e.g., 13 entities) to obtain the signal peak values at left and right sides. This results in low efficiency of incline angle determination. An inactive area on the periphery of the digitizer is large and the range of effective area is limited.